The objective of this research is to establish whether lampbrush chromosome loops have tandemly-repeating sequences and if this is so, to discover whether a single mutational event alters all of the tandem copies. Our approach will be to study the pattern of loop preservation after terminal digestion with various restricting endonucleases. The length distribution of broken loop segments will be measured. If all loops contain tandemly-repeating sequences, then loops will be either totally spared, or totally broken by a given sequence-specific nuclease. Different restricting endonucleases will be unable to break different loops. Those that are broken should be broken into units of a fixed length corresponding to the tandem repeat length. Alternatively, if loops contain non-repeating sequences, all of them should be broken by nearly any restricting endonuclease available, and the distribution of loop fragment lengths should be random - not modular. Having established the basic pattern of loop resistance with a standard variety of Triturus viridescens, we intend to look for polymorphisms, or to make F1's from appropriate related strains. Mutation studies will be initiated at that time to see if a single mutation changes the endonuclease sensitivity of the entire loop.